login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A020453 Primes that contain digits 1 and 5 only. 5
5, 11, 151, 1151, 1511, 11551, 15511, 15551, 51151, 51511, 51551, 55511, 115151, 511111, 511151, 515111, 1111151, 1115551, 1155151, 1551551, 1555111, 5115511, 5151151, 5151551, 5155511, 5511151, 5511511, 5515151, 5551111, 15511151 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first 8 terms are also primes when read backward, i.e. in A007500. See also A199325. - M. F. Hasler, Nov 05 2011

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

MATHEMATICA

Flatten[Table[Select[FromDigits/@Tuples[{1, 5}, n], PrimeQ], {n, 7}]] (* Vincenzo Librandi, Jul 27 2012 *)

PROG

(PARI) {L=[1, 5]; for(d=1, 9, u=vector(d, i, 10^(d-i))~; forvec(v=vector(d, i, [1, #L]), ispseudoprime(t=vector(d, i, L[v[i]])*u)&print1(t", ")))}  \\ - M. F. Hasler, Nov 05 2011

CROSSREFS

Sequence in context: A266527 A267078 A276511 * A036932 A162252 A179388

Adjacent sequences:  A020450 A020451 A020452 * A020454 A020455 A020456

KEYWORD

nonn,base

AUTHOR

David W. Wilson

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 9 17:18 EST 2019. Contains 329879 sequences. (Running on oeis4.)